The humble bundle unique link should provide you with a option to retrieve a code for steam. If you haven't used it before that should work. Hope this helps! I'm actually not seeing a code on the humble bundle page to redeem it on steam. I know i didn't use it before nor have i given the code to anyone else. This is pretty much what i get: I know that the Steam link wouldn't be removed from the list of games i have, because i know i used the steam code for Indie Game: The movie and it wasn't removed.
A while ago I got the Dungeon defenders + all the DLC through the Humble Bundle a while back. I already had the original Dungeon Defenders on my steam account, but none of the DLC. Would I be able to put the DLC from the humble bundle pack on my Steam version, or should i just move my character save from the steam version of the game to the other version?